In recent years, in the field of automatic transmission, there are attempts to design multi-speed automatic transmissions to improve the fuel efficiency. For example, Patent Document 1 discloses an automatic transmission including four planetary gear sets and five frictional engagement elements coaxially with an input shaft to provide eight forward gears and one reverse gear. In this Patent Document 1, a first planetary gear set, a third planetary gear set, a fourth planetary gear set (of a double pinion type), and a second planetary gear set are arranged along the axis of the automatic transmission in this order from one axial end of the automatic transmission. The input shaft is always coupled to a carrier of the first planetary gear set. An output is always coupled to a ring gear of the fourth planetary gear set.